Ethanol can be produced from grain-based feedstocks (such as corn), cellulosic feedstocks (such as switchgrass or corn cobs), or other plant material (such as sugar cane).
In a conventional ethanol plant producing ethanol from corn, corn kernels are processed to separate the starch-containing material (e.g. endosperm) from other matter (such as fiber and germ). The starch-containing material is then slurried with water and liquefied to facilitate saccharification where the starch is converted into sugar (i.e. glucose) and fermentation where the sugar is converted by an ethanologen (i.e. yeast) into ethanol. The product of fermentation is beer, which comprises a liquid component containing ethanol and water (among other things) and a solids component containing unfermented particulate matter (among other things).
According to the process typically used at a conventional ethanol plant, the liquefaction of the starch-containing material is done by “cooking” the slurry at temperature at or near boiling point of water. According to an alternative process (that has been developed and implemented by the assignee of the present application), for example, as described in U.S. Patent Application Publication No. 2005/0239181, raw starch may be converted and fermented without “cooking” or liquefication.
In a conventional ethanol plant, the liquid component and solids component of the fermentation product is sent to a distillation system. In distillation, the fermentation product is processed into, among other things, ethanol and stillage containing wet solids (i.e. the solids component of the beer with substantially all ethanol removed) formed into a wet cake which can be dried into distillers dried grains (DDG) and sold as an animal feed product. Other co-products, for example, syrup (and oil contained in the syrup) can also be recovered from the stillage. Water removed from the fermentation product in distillation can be treated for re-use at the plant.
In a conventional ethanol plant, certain plant operations are conducted at elevated temperatures over ambient temperature with the resultant consumption of energy. For example, the liquefaction of the starch-containing slurry is typically done with a jet cooker (using natural gas as a fuel to elevate the temperature of the slurry to a boil). The amount of energy used in the distillation process (another operation performed at an elevated temperature, with heat typically provided by steam from an on-site boiler) is a function, among other things, the volume/mass of material supplied to the distillation system. The drying of wet solids into distillers dried grains, an operation in which water is removed from the solids typically in a dryer (such as a ring dryer) heated by natural gas, will consume energy as a function of the properties (e.g. heat capacity, heat of vaporization and boiling point) of the water to be removed from the solids.
It would be advantageous provide for a system for producing ethanol that facilitates an overall reduction in the use of energy at the plant, for example, by reducing the mass of wet solids supplied to the distillation system. It would also be advantageous to provide for a system for producing ethanol that reduced the amount of energy used to dry the wet solids component of the fermentation product. It would further be advantageous to provide for a system for producing ethanol that facilitated the recovery of co-products including bioproducts and other biochemicals extracted from components of the fermentation product. It would further be advantageous to provide for a system for producing ethanol in which the solids component of the fermentation product would be dried and constituted into a meal that could be used for animal feed, among other uses.